Search results for "ToP"
showing 10 items of 17685 documents
Ultra- and microplankton assemblages as indicators of trophic status in a Mediterranean lagoon
2016
International audience; The seasonal abundance distribution of heterotrophic prokaryotes, pico-and nanophytoplankton, was investigated in connection with environmental variables and microplankton abundance at five stations in Ghar El Melh Lagoon (northeastern Tunisia). Flow cytometry analysis of ultraplankton resolved (i) five heterotrophic prokaryote groups labelled LNA1, LNA2 (low nucleic acid content), HNA1, HNA2 and HNA3 (high nucleic acid content) and (ii) at least 14 ultraphytoplankton groups assigned to picoeukaryotes, picoprokaryotes, nanoeukaryotes, cryptophyte-like cells and some unknown communities. Redundancy analysis (RDA) revealed (i) autumn-summer outbreaks of heterotrophic p…
Phytoplankton colonization patterns. Is species richness depending on distance among freshwaters and on their connectivity?
2015
Phytoplankton assemblages in two Sicilian water bodies were compared to test the hypothesis that colonization events and the successful establishment of a new species in an aquatic ecosystem may depend on the number of water bodies in a given area and on their relative distance. The two ecosystems are both natural, shallow lakes and they are protected sites hosting a rich avifauna. Lake Biviere di Gela is located in an area with a high density of ponds, whereas Lake Pergusa is an isolated waterbody without other aquatic ecosystems in its surroundings. Both lakes had almost disappeared about 10 years ago because of the over-exploitation of their main inflows. They were therefore re-filled us…
Phytoplankton assemblages in a complex system of interconnected reservoirs: the role of water transport in dispersal
2017
Phytoplankton in a complex network of reservoirs for drinking water supply was sampled in the dry and flood seasons to understand the role of dispersal through hydrochory and of environmental filters in determining the phytoplankton abundance and composition. The main assumptions tested in the present study are that (i) phytoplankton structure in these waterbodies is strongly dependent on the transportation with the river waters flowing through them and (ii) the importance of this stochastic transportation is decreasing as the connectivity with the river decreases allowing environmental filters to shape phytoplankton structure. The multivariate analysis showed that although phytoplankton wa…
Nucleotide Variability at the Acetyl Coenzyme A Carboxylase Gene and the Signature of Herbicide Selection in the Grass Weed Alopecurus myosuroides (H…
2004
Acetyl coenzyme A carboxylase (ACCase) is the target of highly effective herbicides. We investigated the nucleotide variability of the ACCase gene in a sample of 18 black-grass (Alopecurus myosuroides [Huds.]) populations to search for the signature of herbicide selection. Sequencing 3,396 bp encompassing ACCase herbicide-binding domain in 86 individuals revealed 92 polymorphisms, which formed 72 haplotypes. The ratio of nonsynonymous versus synonymous substitutions was very low, in agreement with ACCase being a vital metabolic enzyme. Within black grass, most nonsynonymous substitutions were related to resistance to ACCase-inhibiting herbicides. Differentiation between populations was stro…
Can Deliberately Incomplete Gene Sample Augmentation Improve a Phylogeny Estimate for the Advanced Moths and Butterflies (Hexapoda: Lepidoptera)?
2011
Abstract This paper addresses the question of whether one can economically improve the robustness of a molecular phylogeny estimate by increasing gene sampling in only a subset of taxa, without having the analysis invalidated by artifacts arising from large blocks of missing data. Our case study stems from an ongoing effort to resolve poorly understood deeper relationships in the large clade Ditrysia ( > 150,000 species) of the insect order Lepidoptera (butterflies and moths). Seeking to remedy the overall weak support for deeper divergences in an initial study based on five nuclear genes (6.6 kb) in 123 exemplars, we nearly tripled the total gene sample (to 26 genes, 18.4 kb) but only in a…
The effects of absolute and relative nutrient concentrations (N/P) on phytoplankton in a subtropical reservoir
2020
Abstract The elemental composition of phytoplankton is a critical factor for primary production and nutrient recycling. The increase anthropogenic nutrient input into freshwater ecosystems is affecting phytoplankton assemblage structure and its stoichiometry. Reservoirs of South China generally show low level of phosphate and it is not clear how phytoplankton can grow and occasionally bloom in such conditions. Therefore, an indoor experiment was conducted to investigate the response of natural phytoplankton communities to 25 levels of supplied nitrogen to phosphorus ratios (N/P), arising from the combination of 5 levels of N and P. Our aim was to check the effects of absolute and relative N…
Spatial dynamics of an invasive bird species assessed using robust design occupancy analysis: the case of the Eurasian collared dove ( Streptopelia d…
2007
Aim The study of the spatial dynamics of invasive species is a key issue in invasion ecology. While mathematical models are useful for predicting the extent of population expansions, they are not suitable for measuring and characterizing spatial patterns of invasion unless the probability of detection is homogeneous across the distribution range. Here, we apply recently developed statistical approaches incorporating detection uncertainty to characterize the spatial dynamics of an invasive bird species, the Eurasian collared dove (Streptopelia decaocto). Location France. Methods Data on presence/absence of doves were recorded from 1996 to 2004 over 1045 grid cells (28 × 20 km) covering th…
Kinetic studies on protoporphyrinogen oxidase inhibition by diphenyl ether herbicides
1991
Diphenyl ethers (DPEs) and related herbicides are powerful inhibitors of protoporphyrinogen oxidase, an enzyme involved in the biosynthesis of haems and chlorophylls. The inhibition kinetics of protoporphyrinogen oxidase of various origins by four DPEs, (methyl)-5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid (acifluorfen and its methyl ester, acifluorfen-methyl), methyl-5-[2-chloro-4-(trifluoromethyl) phenoxy]-2-chlorobenzoate (LS 820340) and methyl-5-[2-chloro-5-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid (RH 5348), were studied. The inhibitions of the enzymes from maize (Zea mays) mitochondrial and etiochloroplastic membranes and mouse liver mitochondrial membranes were com…
Characterization of (3H) acifluorfen binding to purified pea etioplasts, and evidence that protoporphyrinogen oxidase specifically binds acifluorfen
1992
It is now generally accepted that protoporphyrinogen oxidase is the target-enzyme for diphenylether-type herbicides. Recent studies [Camadro, J-M., Matringe, M., Scalla, R. & Labbe, P. (1991) Biochem. J. 277, 17–21] have revealed that in maize, diphenyl ethers competitively inhibit protoporphyrinogen oxidase with respect to its substrate, protoporphyrinogen IX. In this study, we show that, in purified pea etioplast, [3H]acifluorfen specifically binds to a single class of high-affinity binding sites with an apparent dissociation constant of 6.2 ± 1.3 nM and a maximum density of 29 ± 5 nmol/g protein. [3H]Acifluorfen binding reaches equilibrium in about 1 min at 30°C. Half dissociation occurs…
Synthesis and properties of a photoaffinity labeling reagent for protoporphyrinogen oxidases, the target enzymes of diphenyl ether herbicides
1994
A diazoketone 3 has been synthesized in two steps from acifluorfen 1, a diphenyl ether herbicide. Like the parent compound 1, the diazoketone 3 is toxic to plant cells and inhibits protoporphyrinogen oxidase, the molecular target of diphenyl ether herbicides. On photolysis of 3 in methanol, the generated carbene mainly undergoes the Wolff rearrangement to a ketene which further adds methanol, but many other products are observed. A tritiated derivative of 3 has been prepared which is suitable for photoaffinity labeling experiments.